Auto merge of #17783 - BorisChiou:stylo/animation/restrictions, r=nox

stylo: Bug 1374233 - Clamp interpolated values for properties which need to be restricted

Some properties only accept non-negative values, or values greater than or equal to one. It is possible to produce an negative interpolated values while using negative timing functions, so we have to apply a restriction to these values to avoid getting invalid values.

For example, line-height must be non-negative, but the output progress of some timing functions (e,g. cubic-bezier(0.25, -2, 0.75, 1)) may be a negative value, so the interpolated result of line-height is also negative.

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix Bug 1374233.
- [X] These changes do not require tests because we have tests in Gecko side already.

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components/style/values/computed/length.rs

@@ -11,6 +11,8 @@ use style_traits::ToCss;
 use style_traits::values::specified::AllowedLengthType;
 use super::{Number, ToComputedValue, Context};
 use values::{Auto, CSSFloat, Either, ExtremumLength, None_, Normal, specified};
+use values::computed::{NonNegativeAu, NonNegativeNumber};
+use values::generics::NonNegative;
 use values::specified::length::{AbsoluteLength, FontBaseSize, FontRelativeLength};
 use values::specified::length::ViewportPercentageLength;
 
@@ -71,7 +73,7 @@ impl ToComputedValue for specified::NoCalcLength {
             specified::NoCalcLength::ViewportPercentage(length) =>
                 length.to_computed_value(context.viewport_size()),
             specified::NoCalcLength::ServoCharacterWidth(length) =>
-                length.to_computed_value(context.style().get_font().clone_font_size()),
+                length.to_computed_value(context.style().get_font().clone_font_size().0),
             #[cfg(feature = "gecko")]
             specified::NoCalcLength::Physical(length) =>
                 length.to_computed_value(context),
@@ -265,7 +267,7 @@ impl specified::CalcLengthOrPercentage {
 
     /// Compute font-size or line-height taking into account text-zoom if necessary.
     pub fn to_computed_value_zoomed(&self, context: &Context) -> CalcLengthOrPercentage {
-        self.to_computed_value_with_zoom(context, |abs| context.maybe_zoom_text(abs))
+        self.to_computed_value_with_zoom(context, |abs| context.maybe_zoom_text(abs.into()).0)
     }
 }
 
@@ -349,6 +351,20 @@ impl LengthOrPercentage {
             },
         }
     }
+
+    /// Returns the clamped non-negative values.
+    #[inline]
+    pub fn clamp_to_non_negative(self) -> Self {
+        match self {
+            LengthOrPercentage::Length(length) => {
+                LengthOrPercentage::Length(Au(::std::cmp::max(length.0, 0)))
+            },
+            LengthOrPercentage::Percentage(percentage) => {
+                LengthOrPercentage::Percentage(Percentage(percentage.0.max(0.)))
+            },
+            _ => self
+        }
+    }
 }
 
 impl fmt::Debug for LengthOrPercentage {
@@ -550,6 +566,43 @@ impl ToComputedValue for specified::LengthOrPercentageOrNone {
     }
 }
 
+/// A wrapper of LengthOrPercentage, whose value must be >= 0.
+pub type NonNegativeLengthOrPercentage = NonNegative<LengthOrPercentage>;
+
+impl From<NonNegativeAu> for NonNegativeLengthOrPercentage {
+    #[inline]
+    fn from(length: NonNegativeAu) -> Self {
+        LengthOrPercentage::Length(length.0).into()
+    }
+}
+
+impl From<LengthOrPercentage> for NonNegativeLengthOrPercentage {
+    #[inline]
+    fn from(lop: LengthOrPercentage) -> Self {
+        NonNegative::<LengthOrPercentage>(lop)
+    }
+}
+
+impl NonNegativeLengthOrPercentage {
+    /// Get zero value.
+    #[inline]
+    pub fn zero() -> Self {
+        NonNegative::<LengthOrPercentage>(LengthOrPercentage::zero())
+    }
+
+    /// Returns true if the computed value is absolute 0 or 0%.
+    #[inline]
+    pub fn is_definitely_zero(&self) -> bool {
+        self.0.is_definitely_zero()
+    }
+
+    /// Returns the used value.
+    #[inline]
+    pub fn to_used_value(&self, containing_length: Au) -> Au {
+        self.0.to_used_value(containing_length)
+    }
+}
+
 /// A computed `<length>` value.
 pub type Length = Au;
 
@@ -573,6 +626,18 @@ impl LengthOrNumber {
 /// Either a computed `<length>` or the `normal` keyword.
 pub type LengthOrNormal = Either<Length, Normal>;
 
+/// A wrapper of Length, whose value must be >= 0.
+pub type NonNegativeLength = NonNegativeAu;
+
+/// Either a computed NonNegativeLength or the `auto` keyword.
+pub type NonNegativeLengthOrAuto = Either<NonNegativeLength, Auto>;
+
+/// Either a computed NonNegativeLength or the `normal` keyword.
+pub type NonNegativeLengthOrNormal = Either<NonNegativeLength, Normal>;
+
+/// Either a computed NonNegativeLength or a NonNegativeNumber value.
+pub type NonNegativeLengthOrNumber = Either<NonNegativeLength, NonNegativeNumber>;
+
 /// A value suitable for a `min-width`, `min-height`, `width` or `height` property.
 /// See values/specified/length.rs for more details.
 #[allow(missing_docs)]